class Solution1 {
    public int peakIndexInMountainArray(int[] arr) {
         if(arr == null) return -1 ;
         int left = 0 ;
         int right = arr.length -1 ;
         while(left < right){
            int mid = left + (right-left+1)/2 ;
            if(arr[mid] >= arr[mid-1] ){
              left = mid ;
            }else{
                right = mid-1 ;
            }
         }
        return left ;

    }
}